1. Field of the Invention
The present invention relates to an image display apparatus employing an electron-emitting device.
2. Related Background Art
In a flat display in which a plurality of electron-emitting devices are arrayed on a flat substrate as an electron source, and an electron beam emitted from the electron source is irradiated at a phosphor which serves as an image forming member on an opposing substrate, whereby an image is displayed by light emitted from the phosphor, it is necessary to maintain to a high vacuum the interior of the vacuum container which encapsulates the electron beam and the image forming member. If the pressure rises in the vacuum container interior due to gases being generated, while the extent of any adverse effects does depend on the type of gas, the electron source is adversely affected and the amount of electrons emitted is decreased, thus rendering it impossible for a bright image to be displayed.
For flat displays especially, gases generated from the image display member accumulate in the vicinity of the electron source before reaching a getter arranged outside of the image display area, thus causing problems characterized by localized pressure rise and the resulting electron source deterioration. Japanese Patent Application Laid-Open No. H09-82245 discloses decreased deterioration or destruction of the devices by providing a getter in the image display region and instantly adsorbing generated gases. Japanese Patent Application Laid-Open No. 2000-133136 discloses a configuration in which a non-evaporating type getter is provided in an image display region and an evaporating type getter is provided outside of the image display region. Further, as disclosed in Japanese Patent Application Laid-Open No. 2000-315458, a series of operations in a vacuum chamber: degassing, getter formation and seal bonding (forming into a vacuum container) has also been devised.
Getters include evaporating type getters and non-evaporating type getters. However, while the exhaust velocity of water or oxygen by an evaporating type getter is extremely large, the exhaust velocity of an inert gas such as argon (Ar) by either an evaporating type getter or a non-evaporating type getter is almost zero. Argon gas is ionized by an electron beam and turned into positive ions, which are accelerated by an electric field whose purpose it is to accelerate electrons, whereby the electron source suffers damage as a result of bombardment of the accelerated ions. In some cases this can cause internal electric discharge, whereby the apparatus can be destroyed.
As an exhaust means which can exhaust noble gases, Japanese Patent Application Laid-Open No. H05-121012 discloses a method wherein a sputtering ion pump is connected to the vacuum container of a flat display for maintaining a high vacuum over a long period of time. As illustrated in FIG. 9, such a thin flat display apparatus comprises a front panel 902 having a fluorescent surface 901 and a container main body 903, which is airtightly sealed therewith and which constitutes a vacuum container 910 together with the front panel 902. An electrode structure 905 is arranged inside this container main body 903. The electrode structure 905 has a field emission cathode, wherein an electron beam emitted from this cathode is modulated by an internal electrode 915 (i.e. a modulating electrode), and directed towards the fluorescent surface 901 for displaying an image. The container main body 903 is connected to an ion pump 908 for vacuum maintenance, whereby the interior of the vacuum container 910 is kept at a pressure of 10−6 Pa (10−8 Torr) or below. As an embodiment of the ion pump 908, 1,000 gauss (0.1 Tesla, hereinafter the unit Tesla of magnetic flux density is indicated by a “T”), for example, is applied using magnetic field generating means 920 for generating a high voltage of from 3 to 5 kV between an anode 912 and a cathode 913, to thereby operate an ion pump 908, whereby an ultra-high vacuum having a pressure of no greater than 10−6 Pa, about 10−8 Pa for example, can be attained.
However, magnetic field leaking from the magnetic field generating means 920 acts on the electron beam whose purpose is to display the image, whereby the beam orbit is changed, thereby causing the beam to deviate when arriving at the phosphor from the location where the beam originally would have arrived. Therefore, there are the problems of members other than the phosphor being bombarded, brightness being reduced due to the beam arriving at an adjacent portion of the phosphor, and color shift occurring in a color image.